It is known and widespread that rotor blade rows of turbines of gas turbines have, at the upper end of the blade airfoils, what is termed a shroud.
A cooled turbine ring segment for a gas turbine is known from US 2004/120803 A1, which segment comprises an axially oriented shroud ring segment having an inner surface, an outer surface, an upstream flange and a downstream flange. The flanges hold the shroud ring in an engine casing. A perforated cooling air impingement plate is arranged on the outer surface of the shroud ring, between the upstream flange and the downstream flange, with an impingement chamber defined between the impingement plate and the outer surface. Axially oriented cooling bores in the ring segment extend between the impingement chamber and an outlet. A hollow adjoining the outlet guides cooling air from the outlet in the direction of a downstream guide vane, in order to cool the guide vane.
EP 0 132 182 A1 shows a seal device for rotor blades of a turbomachine. The seal device comprises section seals. These are, on one hand, attached to an inner ring by means of connection elements and, on the other hand, attached to an outer ring by means of hooks. The inner ring has low thermal inertia and the outer ring has increased thermal inertia. Moreover, the section seals have support ribs on the hooks and centering means.
GB 2 206 651 A presents a turbine blade shroud arrangement which, in operation, surrounds the ends of one stage of turbine blades in a gas turbine engine. The shroud arrangement comprises a ring, which is loosely retained in the axial and radial directions, on a fixed engine structure, a turbine blade shroud having multiple segments abutting laterally against one another, each being hung from a radial face of the ring and positioned in gas sealing and having a relatively movable relationship with respect to the fixed engine structure, wherein the ring is constructed from a material which has slower thermal reaction characteristics than the material of the fixed engine structure.
EP 2 458 152 A2 discloses an axial-flow gas turbine comprising a rotor with alternating rows of air-cooled rotor blades and rotor heat shields, and a stator with alternating rows of air-cooled guide vanes and stator heat shields, which are mounted on inner rings. The stator surrounds the rotor coaxially such that a hot gas path is defined between the stator and the rotor. The rows of rotor blades and stator heat shields, or the rows of guide vanes and rotor heat shields, are arranged opposite one another. One row of guide vanes and the following, downstream row of rotor blades define a turbine stage. The rotor blades are provided with outer blade platforms at their tips. The blade platforms comprise, on their outer side, multiple teeth which run parallel to one another in the circumferential direction and are arranged one behind the other in the direction of the hot gas flow.
The shroud makes it necessary, during work on the rotor blade row which for example takes place for maintenance or testing purposes, to perform what is referred to as a cover lift, that is to say lifting the entire upper casing part. A cover lift is very onerous.